The blockage of an arterial vessel produces ischemia in the tissue normally nourished by the occluded vessel. If the blockage is removed permitting reperfusion of the affected area after greater than sixty minutes of ischemia, further injury, called reperfusion injury, is paradoxically observed. This reperfusion injury is associated with a number of biochemical and physiological events such as release of intracellular enzymes, transient rise in blood pressure, reduction in contractility, influx of calcium, disruption of cell membranes, and eventual tissue necrosis (see Ferrari, et al., Am. J. Clin. Nutr. 53:2158 (1991)). It is thought that much of the tissue damage arising during ischemia and reperfusion results from the chemical action of excess amounts of accumulated oxygen free radicals (Lefer, et al., Basic Res. Cardiol., 86 Suppl. 2:109 (1991); Kirsh, et al., J. Neurotrauma, 9 Suppl. l:S157 (1992); and Bolli, Cardiov. Drugs and Ther., 5:249 (1991)).
Experiments in a number of animal models have investigated the use of antioxidants or enzymes to control reperfusion injury. For example, Weyrich, et al., Circulation, 86:279 (1992) showed that administration of L-arginine reduced necrotic injury in a cat model of myocardial infarction. McMurray et al., J. Clin. Pharmac., 31:373 (1991) investigated sulfhydryl containing angiotensin converting enzyme inhibitors. Naslund, et al., Circ. Res., 66:1294 (1990) concluded from their work on a swine coronary model, that infarct size could be limited by administration of superoxide dismutase, but only during a very narrow window of time post-infarction. Schaer, et al., JACC, 15:1385 (1990) report a reduction in reperfusion injury by administering an acellular oxygenated perfluorochemical emulsion called Fluosol.
An important model system is percutaneous transluminal coronary angioplasty in the pig. McKenzie, et al., Cardiovascular Research, xe2x80x9cEffects of diaspirin cross-linked hemoglobin during coronary angioplasty in the swinexe2x80x9d, 28(8):1188-1193 (1994) utilized this technique to study the effects of temporary regional myocardial ischemia. They inserted a catheter into the proximal left anterior descending coronary artery and inflated the catheter balloon to occlude the artery for a period of 4 minutes. A significant reduction in cardiac function compared to controls was observed as measured by mean arterial blood pressure (MAP), peak systolic left ventricular pressure (IVP), rate of left ventricular pressure development (dP/dt), pressure rate product (PRP), and cardiac output (CO). In addition, electrocardiograms showed elevation of the S-T segment of the ECG. These experiments are significant because McKenzie, et al. compared controls to animals receiving infusions of hemoglobin, and found that cardiac function increased significantly and the S-T segment of the ECG returned toward baseline.
The concept of infusing hemoglobin products as a substitute for blood has a long history (for a historical perspective, see R. M. Winslow, xe2x80x9cHemoglobin-based Red Cell Substitutesxe2x80x9d, The Johns Hopkins University Press, 1992). Free hemoglobin is not suitable for this purpose since oxygen is bound too tightly to be released in the tissues. Also, hemoglobin monomers are rapidly cleared from the blood and exhibit renal toxicity. Better success has been achieved with chemically modified hemoglobins, which assume a conformation allowing release of oxygen, and whose size and stability are more resistant to clearance.
Hemoglobins may be alpha alpha cross-linked as disclosed in U.S. Pat. No. 4,600,531 and RE 34,271 (Walder), and virus inactivated and purified as taught in U.S. Pat. No. 4,831,012 (Estep). Modification by pyridoxyation, carbamylation, or carboxymethylation is also known, as are chemical schemes for both cross-linking and polymerizing, as by glutaraldehyde. A summary of these chemistries is contained in Winslow, supra.
This invention provides a method for treating blockage of a blood vessel, which may be a thrombus, fat embolus, plaque, or other obstruction, or restenosis at remote times of a previously blocked vessel, which comprises administering, generally by intravenous infusion, hemoglobin to a patient undergoing tissue ischemia. There are different ways of defining the therapeutically efficacious dose which may be administered. An amount of hemoglobin may be administered which is sufficient to suppress or reduce reperfusion injury to the tissue whose nourishment has been disrupted by the blockage. These doses are effective not only to delimit the amount of infarcted tissue as a percentage of the cardiac tissue at risk during occlusion, but also for preventing restenosis of the vessel after the original blockage has been relieved. This protection effect is also measured by the reduction in number, magnitude, and duration to onset of ventricular arrhythmias which are known to precipitate sudden cardiac arrest in a significant proportion of patients suffering myocardial infarction. This protection is further measured by improved regional myocardial function in the border zone. Thus, the present invention affords a method for improving contractile function in ischemic cardiac tissue following relief of heart vessel blockage comprising administering hemoglobin in a dose effective to obtain a wall motion score improvement of at least 0.15 relative units between the infarct zone and 20 chords in the tissue region at risk. An effective amount is in the range of 10-2500 mg/kg of body weight, preferably 75-750 mg/kg.
The present invention thus provides a method of reducing the frequency and duration to onset of cardiac arrhythmias following relief of cardiac arterial blockage by administering hemoglobin generally in a like dose. This method also results in reducing the incidence of restenosis of a blood vessel at remote times after relief of a blockage thereof by administering hemoglobin in a like dose, which generally falls within the range of 10-2500 mg/kg of body weight, preferably 75-750 mg/kg.
The benefits and objects of administering hemoglobin as a treatment for blood vessel blockage are that it increases salvage of the area at risk, it stabilizes the circulatory system, as in cardiac ischemia, and may act directly or indirectly to lower levels of free oxygen radicals and other molecular species associated with tissue damage. It also ameliorates injury to an occluded vessel associated with restenosis of the vessel at remote times up to several weeks or longer. Many of hemoglobin""s pharmacological properties are not yet understood mechanistically. It would appear that some of these properties are unrelated to oxygen-delivery since the effects are exerted at hemoglobin doses which are too low to make a significant impact on this parameter.